Table_1_Quantifying the combined impacts of anthropogenic CO2 emissions and watershed alteration on estuary acidification at biologically-relevant time scales: a case study from Tillamook Bay, OR, USA.docx

The impacts of ocean acidification (OA) on coastal water quality have been subject to intensive research in the past decade, but how emissions-driven OA combines with human modifications of coastal river inputs to affect estuarine acidification dynamics is less well understood. This study presents a methodology for quantifying the synergistic water quality impacts of OA and riverine acidification on biologically-relevant timescales through a case study from a small, temperate estuary influenced by coastal upwelling and watershed development. We characterized the dynamics and drivers of carbonate chemistry in Tillamook Bay, OR (USA), along with its coastal ocean and riverine end-members, through a series of synoptic samplings and continuous water quality monitoring from July 2017 to July 2018. Synoptic river sampling showed acidification and increased CO2 content in areas with higher proportions of watershed anthropogenic land use. We propagated the impacts of 1). the observed riverine acidification, and 2). modeled OA changes to incoming coastal ocean waters across the full estuarine salinity spectrum and quantified changes in estuarine carbonate chemistry at a 15-minute temporal resolution. The largest magnitude of acidification (-1.4 pHT units) was found in oligo- and mesohaline portions of the estuary due to the poor buffering characteristics of these waters, and was primarily driven by acidified riverine inputs. Despite this, emissions-driven OA is responsible for over 94% of anthropogenic carbon loading to Tillamook Bay and the dominant driver of acidification across most of the estuary due to its large tidal prism and relatively small river discharges. This dominance of ocean-sourced anthropogenic carbon challenges the efficacy of local management actions to ameliorate estuarine acidification impacts. Despite the relatively large acidification effects experienced in Tillamook Bay (-0.16 to -0.23 pHT units) as compared with typical open ocean change (approximately -0.1 pHT units), observations of estuarine pHT would meet existing state standards for pHT. Our analytical framework addresses pressing needs for water quality assessment and coastal resilience strategies to differentiate the impacts of anthropogenic acidification from natural variability in dynamic estuarine systems.</p

Target and Measured DIC and Total Alkalinity.

<p>The target and measured values of total alkalinity and total dissolved inorganic carbon (DIC) in μmol kg^-1. The 1:1 line represents if our measured measured values were exactly aligned with the target values.</p

Proportion Normal Shell Development.

<p>The proportion of normally developed shells in relation to (A) P_CO2, (B) pH, and (C) Ω_aragonite. Greyscale symbols denote Ω_ar treatments in panels A and B, and the star is the control treatment. Error bars are standard deviations of the three replicate BOD bottles per treatment. See text for fit of model noted on panel C.</p

Comparisons Among Respiration Treatments.

<p>Respiration rates presented on a bar graph showing pairwise comparisons across all treatments, with the common line over values representing no significant difference. Error bars are standard errors. Note that values are arranged in increasing pH along the x-axis, and P_CO2 and Ω_ar are included for each treatment. All values are in units previously noted.</p

Normal Shell Length.

<p>Shell length of normally developed larvae (48 hours post fertilization and exposure) in relation to (A) P_CO2, (B) pH, and (C) Ω_aragonite. Greyscale symbols denote Ω_ar treatments in panels A and B, and the star indicates control data. Error bars are standard deviations of the three replicate BOD bottles per treatment. See text for fit of model noted on panel C.</p

Experimental Carbonate Chemistry Treatments.

<p>Carbonate chemistry treatments of Ω_ar and P_CO2 (μatm), with pH (total) isopleths to illustrate the relationship among the three variables in the experiments. Grey circles are the actual treatment values, and star indicates the treatment chemistry of the control (freshly collected seawater bubbled with CO₂-reduced air for 24 hours).</p

Complete Carbonate Chemistry.

<p>Experimental salinity and temperature were 31 and 18^°C, respectively. Primary treatment levels for saturation state and P_CO2 are noted in the left two columns. Total alkalinity (Talk), Dissolved inorganic carbon (DIC), Bicarbonate ion (HCO₃), Carbonate ion (CO₃) are all reported in μmol kg^-1. P_CO2 is in μatm. Treatment (trt) combinations in bold indicate those used for the respiration rate measurements. Asterisk denotes a preservation problem with this sample, and therefore P_CO2 was greatly elevated relative to the initial treatment. The control was freshly seawater bubbled with CO₂-reduced air for 24 hours.</p><p>Carbonate chemistry of experimental treatments and control.</p

Initiation of Larval Feeding.

<p>The proportion of larvae feeding 44 hours post-fertilization and exposure in relation to (A) P_CO2, (B) pH, and (C) Ω_aragonite. Greyscale symbols denote P_CO2 treatments in panels B and C. Error bars are standard deviations of the three replicate experimental containers per treatment. Bold value on panel B indicates the significant linear relationship between pH and initiation of feeding for the high P_CO2 treatment. As noted in the text, the removal of this high P_CO2 treatment results in extremely poor fit of the response to pH.</p

Shell Development ANOVA Table.

<p>The magnitude of the factor effect is estimated by η², a measure of relative importance of parameters in the model calculated by SS_effect/SS_total.</p><p>Analysis of variance of shell development data in response to the primary factors in the experiment, Ω_ar and P_CO2.</p